Design and evaluation of layered diffusional matrices for zero-order sustained-release.

New layered matrix systems designed for zero-order sustained release are presented. The devices consist of a hydrophobic middle layer and press-coated hydrophillic and/or hydrophobic barrier layer(s). The systems overcome the inherent disadvantage of non-linear release associated with diffusion-controlled matrix devices by providing additional releasing surface with time to compensate for the decreasing release rate. The in vitro release of pseudoephedrine hydrochloride as a model compound from the matrices was examined. Modulation of release from a selected matrix containing aminophylline was evaluated in a crossover study using nine beagle dogs. Preliminary in vitro/in vivo correlation was also studied. The systems described in this paper can potentially be scaled up to commercial production.